In automobile engines or fuel cell stacks, a fluid or coolant is typically used to carry excess heat from the engine to the radiator. Usually, such coolant is continuously circulated by a pump, through the engine/stack until its temperature exceeds a predetermined level, at which point a portion of the flow is routed through the radiator. The flow is continuously adjusted in an attempt to maintain the temperature of the engine/stack within a desired range. In the context of internal combustion engines, this is often done via a valve that is actuated by a wax motor that is immersed in the flow.
In a known prior art fluid circuit, the radiator and a closure valve are connected in series in the coolant circuit, and a bypass circuit is connected in parallel across the radiator and closure valve. The valve is configured so as to block the flow of coolant through the radiator when the valve is closed. When the valve is closed, the coolant continues to circulate through the engine via the bypass circuit. A disadvantage associated with this configuration is that the bypass flow path remains open at all times such that a substantial portion of the flow of coolant always bypasses the radiator, even if maximum cooling is called for.
Various valves form part of the prior art.
To avoid the problems associated with a permanent bypass flow, these valves provide for the selection between a heat exchanging fluid circuit, which passes through the radiator, and a non-heat exchanging fluid circuit, which short circuits or bypasses the radiator. (In the context of traditional internal combustion engine vehicles, the bypass loop is often the heater core circuit, which is technically also a heat exchanging fluid circuit, so that there is always coolant flow through the heater core. The option to provide or not provide heat to the passenger cabin is achieved via manual or vacuum operated valve control of ducting of the air flow through or around the heater core.).
However, known valves are either relatively expensive, relatively non-robust, or have relatively poor flow characteristics.